Deformation twinning and dislocation processes in nanotwinned copper by molecular dynamics simulations

Nanotwinned materials exhibit a combination of high strength and good ductility which is attributed to the interactions between dislocations and twin boundaries. But no attempt has been made to explore the possibility for deformation twinning in nanotwinned face-centered cubic materials. Here we use large scale molecular dynamics simulations to elucidate the mechanical behaviour of nanotwinned Cu. We demonstrate that deformation twinning plays an important role in the deformation of nanotwinned Cu with specific twin orientations, in addition to conventional dislocation slip. Deformation twins are formed through the glide of Shockley partials on adjacent {1  1  1} slip planes and two twinning mechanisms are identified based on the arrangement of Shockley partials. The first mechanism involves the successive motion of Shockley partials of different types, named as double-Shockley partials, which forms unstable thin twin plates. The second process involves the successive passage of the same twinning dislocations on neighbouring slip planes, which forms stable deformation twins along one primary twinning system or symmetric twinning systems. The dislocation processes involved in the dislocation-twin reactions are analysed at atomic level. The orientation dependence of deformation twinning is discussed and compared with available experimental results.